1. Field of the Invention
The present invention relates to absorbent structures and absorbent garments formed from the structures. Specifically, the present invention relates to absorbent structures comprising relatively high concentrations of a superabsorbent material and to absorbent garments which comprise relatively small absorbent structures.
2. Description of the Related Art
Absorbent structures suitable for use in absorbent garments such as diapers, adult incontinent products and the like are known. Such absorbent structures are described, for example, in U.S. Pat. No. 4,699,619 issued Oct. 13, 1987 to Bernardin; U.S. Pat. No. 4,798,603 issued Jan. 17, 1989 to Meyer et at.; and U.S. Pat. No. 4,834,735 issued May 30, 1989 to Alemany et al. Generally, such absorbent structures comprise a fibrous matrix and, optionally, a high-absorbency material. The fibrous matrix is suitable formed from airlaid cellulosic fibers such as those fibers commonly known as wood pulp fluff, or a coform material comprising cellulosic fibers and meltblown polyolefin fibers. A wide variety of high-absorbency materials are known to those skilled in the art. See, for example, U.S. Pat. Nos. 4,076,63 issued Feb. 28, 1978 to Masuda et al; 4,286,082 issued Aug. 25, 1981 to Tsubakimoto et al.; 4,062,817 issued Dec. 13, 1977 to Westerman; and 4,340,706 issued Jul. 20, 1982 to Obayashi.
Known absorbent structures generally comprise a relatively low amount (less than about 50 weight percent) of the high-absorbency material. There are several reasons for this. For example, high-absorbency materials employed in known absorbent structures have generally not had an absorption rate which would allow them to absorb liquid at the rate at which the liquid is applied to the absorbent structures during use. Accordingly, the fibrous matrix must serve as a reservoir which will hold the liquid discharged thereon until the liquid is absorbed by the high-absorbency material. Additionally, many of the known high-absorbency materials, particularly the synthetic high-absorbency materials, have exhibited gel blocking. Gel blocking refers to the situation wherein the particles of high-absorbency material deform during swelling and block the interstitial spaces between the particles or between the particles and the fibrous matrix thus preventing the flow of liquid through the interstitial spaces. At lower levels of addition the fibrous matrix serves to keep the particles of high-absorbency material separated from one another and provides a capillary structure which allows a liquid to pass through the fibrous matrix to reach high absorbency materials located remote from the point at which the liquid is applied to the absorbent structure.
Dispersing such high-absorbency materials in a fibrous matrix at relatively low concentrations in order to avoid gel blocking resulted in the need to locate high-absorbence materials in areas relatively remote from the point at which the liquid is applied to the absorbent structure. That is, in order to introduce useful amounts of high-absorbency material into an absorbent structure and yet disperse such high-absorbency materials sufficiently to prevent gel blocking, it was necessary for the absorbent structures to have relatively large surface areas and to be relatively thick.
Alternatively, it was necessary to design multi-component systems in an attempt to compensate for the problems associated with employing higher concentrations of high-absorbency material. See, for example, U.S. Pat. No. 4,673,402 issued Jun. 16, 1987 to Weisman et al. which describes a dual layered absorbent core. The upper layer is a fluid acquisition layer containing up to 8 percent of a high-absorbency material. The lower layer is a fluid storage layer containing up to 60 weight percent of a high-absorbency material. The upper layer is present to absorb and hold a liquid until the lower layer can absorb the liquid.
Since a liquid to be absorbed by an absorbent structure is generally applied to the structure in a relatively localized area, it became necessary to devise ways in which to move the liquid to be absorbed from the point of application to remote areas of the absorbent structure for absorption by the high-absorbency materials. This need precipitated the use of various structures and methods which are described as being capable of distributing a liquid throughout the absorbent structure. See, for example. U.S. Pat. No. 4,699,619 issued Oct. 13, 1987, to Bernardin; U.S. Pat. Nos. 2,952,260, 2,955,641, 3,017,304, 3,060,936, and 3,494,362 to Burgeni; U.S. Pat. No. 4,103,062 to Aberson; and U.S. Pat. No. 4,397,644 to Matthews et al. Use of such structures and methods further contributed to the size and thickness of the absorbent structures.
Prior to the use of high-absorbency materials in absorbent structures, it was general practice to form absorbent structures such as those suitable for use in infant diapers, entirely from wood pulp fluff. Given the relatively low amount of liquid absorbed by wood pulp fluff on a gram of liquid absorbed per gram of wood pulp fluff (about 7-9 g/g saturated retention capacity), it was necessary to employ relatively large quantities of wood pulp fluff, thus necessitating the use of relatively large, thick absorbent structures. The introduction of high-absorbency materials into such structures allowed for the use of less wood pulp fluff, since the high-absorbency material has a significantly higher absorption capacity on a gram per gram basis (at least about 15 g/g saturated retention capacity). Moreover, such high-absorbency materials are less pressure sensitive than wood pulp fluff. Thus, the use of the high-absorbency materials allowed for the production and use of a smaller, thinner absorbent structure. Nonetheless, for the above reasons, it was still necessary to use relatively low concentrations of superabsorbent material and enough fibrous matrix to permit the high-absorbency materials to function in the desired manner.
It is generally desired that absorbent garments such as diapers be able to rapidly absorb multiple insults of urine during use. Typically, diapers have been produce with absorbent capacities greater than the actual in-use needed capacity. This surplus capacity was believed necessary to achieve the desired performance (lack of leakage or low level of skin wetness) by the diapers. For example, if it was anticipated that a given diaper needed to be able to absorb 250 milliliters of urine in-use, the diaper may have been designed with an absorbent capacity of 400 milliliters or more. The excess capacity was necessary to compensate for the inability of the absorbent medium to absorb the urine at in-use delivery rates and under in-use delivery conditions. The practice of building in excess absorbent capacity is inefficient and undesirable.